Semiconductor anode photomultiplier tube

Abstract

A photomultiplier tube in which the a semiconductor photodiode serves as the anode and receives the electrons from the photocathode. The particular geometry for the focusing electrodes in the tube involves a two part structure with one part, the anode focus electrode, in close proximity to the semiconductor photodiode. The second part of the focus structure is a grid focus electrode with two different diameters, located approximately midway between the photodiode and the photocathode and operating on a low voltage. Together the electrodes create a focusing electric field so that the electrons from the large area photocathode are efficiently delivered to the small area of the semiconductor photodiode. The mounting of the photodiode is also designed to act as a termination to furnish superior timing characteristics.

What is claimed as new and for which Letters patent of the United States are desired to be secured is: 
     
       1. A photomultiplier tube comprising: a sealed envelope from which all gases have been evacuated to form a vacuum suitable for operation of a electron tube within the sealed envelope;   a window which forms a part of the sealed envelope and through which radiation can pass;   a photocathode located on the inside surface of the window, the photocathode emitting electrons when affected by radiation passing through the window, the photocathode having a first voltage applied to it;   a semiconductor photodiode located within the sealed envelope and having a second voltage applied to it, the semiconductor photodiode generating an electrical signal on output connections when it is contacted by electrons from the photocathode, with the electrical signal varying with the quantity of electrons contacting the semiconductor photodiode;   at least an anode focus electrode and a grid focus electrode located within the sealed envelope in the region between the photocathode and the semiconductor photodiode with the anode focus electrode being nearer to the semiconductor photodiode, the focus electrodes being formed of electrically conductive material and having a third electrical voltage applied to the grid focus electrode and a fourth electrical voltage applied to the anode focus electrode so that a focus electrical field is formed within the sealed envelope to direct electrons leaving the photocathode to the semiconductor photodiode.   
     
     
       2. The photomultiplier tube of claim 1 wherein the photocathode, the semiconductor photodiode, and the focus electrodes are oriented in a coaxial configuration. 
     
     
       3. The photomultiplier tube of claim 1 wherein the output connections of the semiconductor photodiode are formed in a configuration which has a specific impedance characteristic which matches the impedance of a circuit external to the photomultiplier tube which is connected to the output connections. 
     
     
       4. The photomultiplier tube of claim 1 wherein the semiconductor photodiode is located on the axis of the photomultiplier tube. 
     
     
       5. The photomultiplier tube of claim 1 wherein the semiconductor photodiode is located at the crossover point of the focus electrical field formed by the voltages applied between it and the photocathode and the focus electrodes. 
     
     
       6. The photomultiplier tube of claim 1 wherein the grid focus electrode is constructed of two segments, the segments having different diameters, and the segment located nearer to the photocathode having a larger diameter. 
     
     
       7. The photomultiplier tube of claim 1 wherein the window is formed with two parallel planar surfaces. 
     
     
       8. The photomultiplier tube of claim 1 wherein the window is formed with a concave inside surface and a planar outside surface. 
     
     
       9. The photomultiplier tube of claim 1 wherein the window is formed with two concave surfaces with the centers of radius of both surfaces being inside the tube.